I appreciate all the feedback.

I have entered the 24 word seed into a Trezor One I had on hand.  It does recover the account showing all their tx history including where they sent the 3 Bitcoin out on December 19, 2017.  But it does not show 3 bitcoin being received.  I also had it display the "Legacy" accounts over on the left of the screen as HCP was showing.  They are all empty. 

I am beginning to think that they acquired the address from some other source and not their Trezor One.  They are quite certain this is not the case.  They assure me they had no other wallets or accounts other then Coinbase and they are not there.

So I am left scratching my head.  The 3 bitcoin are in the address they sent me in their email back in 2017. They say it came from the Trezor One.  They say they saw the 3 bitcoin I sent back to them show up in the "Legacy Account" on the Trezor One but that they were greyed out.  They were unable to send them any where.  Then after they updated the firmware they claim the bitcoins quit showing up in the legacy account even as greyed out ones.  It is not clear to me whether the actual firmware update caused them to disappear or whether the cookies on their computer that had knowledge of the bitcoin expired.  But if the Ledger software was showing the coins as greyed out coins in a legacy account then surely the address came from the ledger?  I have both seed phrases they claimed to have used with the Trezor One.  They are adamant that there were no other seed phrases ever used.  The 12 word phrase first then later they re-set the trezor and used the 24 word phrase it gave them.  For what it's worth the 24 word seed phrase shows the history of them sending me the 3 Bitcoin.  So I feel when I returned it to them a few weeks later they would have given me an address out of the trezor using the 24 word seed.  But even if the address came from the 12 seed phrase it should show up when I recover it.  And the 3 bitcoins do not show up on the Trezor One in any of the accounts including the legacy account for either seed phrase.

So I am stumped.

At this point I am simply going to try crafting a manual bitcoin transaction using a private key derived from the 24-word seed phrase and see if when submitted the bitcoin network will move the coins for me.

I'll keep you posted as to any outcomes I achieve.

Thank you for taking the time to help out.